1. Field of the Invention
The present invention relates to a process and an apparatus for reducing a picture with prevention of fine line disappearance. The process and apparatus according to the present invention are applicable to facsimile picture transmission.
2. Description of the Related Art
In general, the reduction or enlargement of a picture is carried out in the conversion of the concentration of picture pixels in connection with the conversion between different facsimile transmission types, such as G3 and G4 prescribed by CCITT standards.
In the prior art, a high speed projection method type picture reduction is used in which the determination of monochrome pixel data, i.e., whether a pixel is black or white, of a reduced picture is carried out by a logic calculation of basic data. In the high speed projection type method, an area of the original picture is divided into sections, a logic calculation formula is provided for each of these sections, and a logic calculation is carried out for each of the reduced picture pixels according to the logic calculation formula so that the monochrome pixel data of the reduced picture is determined.
However, in the prior art picture reduction process, such as the high speed projection method type picture reduction process, there is a problem of a disappearance of fine lines. That is, a vertical line having a width of less than 1/p where p is the reduction rate along the X-axis, and a horizontal line having a width of less than 1/q where q is the reduction rate along the Y-axis, will disappear in the reduction process. This causes a serious disadvantage in the picture reduction in the technique of the conversion of the concentration of picture pixels in connection with the conversion between different facsimile transmission types.